Semiconductor light emitting devices such as light emitting diodes (LEDs) are among the most efficient light sources currently available. Material systems currently of interest in the manufacture of high brightness LEDs capable of operation across the visible spectrum include group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials; and binary, ternary, and quaternary alloys of gallium, aluminum, indium, arsenic, and phosphorus. Often III-nitride devices are epitaxially grown on sapphire, silicon carbide, or III-nitride substrates and III-phosphide devices are epitaxially grown on gallium arsenide by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. Often, an n-type region is deposited on the substrate, then a light emitting or active region is deposited on the n-type region, then a p-type region is deposited on the active region. The order of the layers may be reversed such that the p-type region is adjacent to the substrate.
FIG. 1 illustrates a semiconductor device 30 described in more detail in US 2008/0081397, which is incorporated herein by reference. Device 30 includes an epitaxial structure 32. The epitaxial structure 32 includes an n-type region 36, which is grown on the substrate 34. The epitaxial structure 32 further includes a light emitting region 38, grown on the n-type region 36, and a p-type region 40, which is grown on the light emitting region 38. In general the n-type region 36, the p-type region 40, and the light emitting region 38 may each include a plurality of layers of different composition and dopant concentration. In one embodiment, where it is desired to remove the substrate 34 after processing, the n-type region 36 may include a release layer (not shown) located between the n-type region and the substrate, for facilitating release of the substrate from the epitaxial structure 32.
A p-metal layer 44, which generally comprises a highly reflective metal, is formed in electrical contact with the p-type region 40. An optional guard layer 46 may be deposited over the p-metal layer 44. The guard layer 46 may be used, for example, when the p-metal layer 44 comprises silver, in which case the guard layer is included to prevent silver from migrating to other parts of the epitaxial structure 32. The guard layer 46 is in electrical contact with the p-metal layer 44. One or more p-electrode metal layers 48 may be deposited over the guard layer 46 and in electrical connection therewith. In the case of a dielectric guard layer, a via hole may be etched through the guard layer to facilitate contact between p-electrode metal layers 48 and p-metal layer 44.
The epitaxial structure 32 further includes one or more voids 50. The voids 50 facilitate electrical connection to the n-type region 36. A dielectric layer 52 is deposited over the guard metal layers 46 and side wall surfaces of the voids 50. The epitaxial structure 32 also includes an n-electrode metal layer 56 deposited over the dielectric layer 52 and the bottom surface of void 50. The n-electrode layer 56 at the bottom of the void 50 is in electrical connection with the n-type region 36, and provides an electrical connection thereto. The dielectric layer 52 electrically insulates the n-electrodes 56 from the p-electrode 48, the guard metal layer 46, and the p-type region 40.
The voids 50 may further include a trench which is operable to electrically insulate the p-electrode 48 from the n-electrodes 56. The voids 50 weaken the semiconductor structure 30, making the structure susceptible to damage during mounting and/or operation. A support material 110 substantially fills the voids 50. The support material 110 is sufficiently solidified to support the semiconductor structure 30 during mounting and/or operation. In one embodiment the support material 110 has a glass transition temperature greater than the operating temperature of the semiconductor light emitting structure 30, such that the support material remains sufficiently rigid to support the semiconductor structure when operating to generate light.
In the embodiment shown the support material 110 overfills the voids 50 and covers at least a portion of an upper surface 112 of the epitaxial structure 32. The support material 110 may be deposited by spin coating a wafer (not shown) including a plurality of semiconductor structures 30. Spin coating involves depositing more than a sufficient quantity of a fluid support material 110, and then spinning the wafer to cause the fluid to form a thin coating over the wafer. Spinning continues until the coating has sufficiently cured through evaporation of solvents, for example. The support material 110 may then be further cured by baking the wafer in an oven to raise the temperature above the support material cure temperature to solidify the support material sufficiently to support the semiconductor structure 30.
Referring to FIG. 2, the process continues by planarizing the wafer. Planarizing may involve mechanical process steps such as lapping the wafer to abrade away excess support material 110. In one embodiment lapping may remove a portion of the n-electrode layer 56 and the p-electrode 48, to provide a substantially flat mounting surface. Mechanical lapping may also be combined with chemical etching.